1. Field of the Invention
The present invention relates to a traveling control device to be applied to construction machinery equipped with a crawler type traveling body like a hydraulic excavator.
2. Description of the Related Art
The prior art will be described hereinafter with hydraulic excavator by way of example.
The conventional traveling control device (a hydraulic circuit) for controlling the operation of the crawler type traveling body in the hydraulic excavator is depicted in FIG. 6.
As shown in FIG. 6, the traveling control device is constituted with a hydraulic motor for a left traveling body 11 and a hydraulic traveling motor for a right traveling body 12 (hereinafter, they are referred to as a left traveling motor, and a right traveling motor). Both traveling motors 11 and 12 are operated by hydraulic pumps 13 and 14 (hereinafter, they are referred to as a left hydraulic pump, and a right hydraulic pump), respectively.
In addition, motor circuits 15 and 16 connect two motors 11 and 12, two (a right and a left) pumps 13 and 14, and a tank T, and hydraulic pilot type control valves 17 and 18 are installed in each circuit. The control valves 17 and 18 are converted and controlled by a remote control pressure from remote control valves 19 and 20 that are operated by levers (or pedals) 19a and 20a. In this way, the rotational direction (forward, backward) and the rotational speed (traveling speed) of both traveling motors 11 and 12 are controlled.
In other words, when the remote control valves 19 and 20 are operated, the control valves 17 and 18 are operated by the stroke in accordance with the control input of the remote control valves, which consequently determining an opening of the valve. And, the flaw rate according to the valve opening is supplied to the traveling motors 11 and 12, raising the pump pressure, and operating the traveling motors 11 and 12.
Incidentally, in the conventional traveling control device, the relation between the control input of the remote control valves 19 and 20 (hereinafter, it is referred to as the control input) and the pump pressure from the reaction manifests exactly the same properties, without any difference in two different cases, such as:
(a) double traveling in which both traveling motors 11 and 12 rotate simultaneously; and
(b) single traveling in which only one of the traveling motors 11 and 12 rotates.
However, during the single traveling, since the load operated by one traveling motor is comparatively larger than that of the double traveling, the control input necessary for the operation gets relatively increased. That is, the double traveling can be traveled even at the slight operation, while the single traveling will not start the traveling unless it is operated deeply.
Therefore, during the single traveling, the control input after the operation is small, causing the micro-operational ability within the range of the control input after the operation to be deteriorated.
On the other hand, if the single traveling at a small control input is possible, this speeds up the operation of the double traveling too much (because of the increased sensitivity of the small control input). In result, the traveling may start suddenly, and the micro-operation at the small control input is deteriorated.
An object of the present invention is to provide a traveling control device for properly applying single traveling as well as double traveling in accordance with its own properties.
The traveling control device of the present invention comprises: a crawler type right and left traveling body; a right and a left hydraulic motors for operating the right and left traveling body, using each hydraulic pump as a hydraulic source; an operating means for outputting an operation command to the both hydraulic motor; and a pump pressure control means for controlling the pump pressure supplied to the double hydraulic motors in accordance with the control input of the operating means. The pump pressure control means controls the pump pressure based on different properties of the pump pressure during the single traveling where only one hydraulic motor is operated, and the double traveling where both hydraulic motors are simultaneously operated.
In the present invention, considering that different properties of pump pressures are applied to the single traveling and the double traveling by the pump pressure control means, the inventors decided to utilize this property of the pump pressure for both single traveling and double traveling by way of improving the operation in overall.
Also, the pump pressure control means of the present invention is devised to control the pump pressure based on the property of the pump pressure, that is, the variation slope of the pump pressure against the control input is greater for the single traveling than for the double traveling.
According to this, the inventors tried to make the variation of the pump pressure be more steep during the single traveling, while be more gentle during the double traveling, trying to improve the micro-operation within the control input after the operation through the greatly increased control input after the operation of the one-side operation. Besides, the present invention can obtain excellent micro-operation even at the small control input during the double traveling. In short, through the present invention, it became possible to obtain excellent manipulation ability for both single traveling and double traveling.
Also, the present invention has a constitution in which said pump pressure control means controls the pump pressure based on a pump pressure property that the control input necessary for a traveling operation for the single traveling and the double traveling is almost equivalent to each other.
According to this, since the control input necessary for the traveling operation becomes almost same for the single traveling and for the double traveling, the manipulation facility thereof gets even better.
Further, the pump pressure control means of the present invention comprises a pressure control valve connected to the motor circuit that connects the hydraulic pump and the hydraulic motor, and a set pressure adjusting means for adjusting the set pressure of the pressure control valve according to the control input of the operating means.
The system aforementioned is particularly for adjusting a set pressure of the pressure control valve out of the control systems to change the properties of the pump pressure during the single traveling and the double traveling.
Also, the pressure control valve of the present invention is a cut valve, which is installed in a bypass line passing through a control valve that controls the operation of the double hydraulic motor. In addition, the pressure control valve throttles the flow rate of the bypass line, and the set pressure adjusting means controls the opening of the cut valve.
The system described above is so called a cut valve control system where the cut valve is used as the pressure control valve, and the opening of the cut valve is controlled eventually for controlling the pump pressure.
Another aspect of the present invention provides the traveling control device using the hydraulic pilot type control valve and cut valve, and a remote control valve as a means for operating the control valve. Also, the set pressure adjusting means of the present invention preferably includes a shuttle valve for withdrawing the remote control pressure from the remote control valve; a cut valve pilot line for connecting the shuttle valve; and a hydraulic pilot port of the cut valve; a hydraulic pilot type traveling switching valve for closing and opening the cut valve pilot line; and a switching valve control circuit for supplying the remote control pressure of the operated side to the traveling switching valve of the opposite side as a pilot pressure to a closing direction of the traveling switching valve.
The system described above is so called a cut valve hydraulic control system that controls the cut valve by the remote control pressure from the remote control valve. Particularly, the system is known for low mechanical trouble rate due to broken wires, and for excellent reliability.
Further, the present invention includes a regulator for regulating the discharge flow rate of the double hydraulic pump, and a negative control valve installed in the bypass line. The negative control valve varies the regulator""s input according to the passing flow rate of the bypass line in order to change the pump discharge flow rate.
According to this, as the passing flow rate of the cut valve changes, the pressure inputted in the pump""s regulator from the negative control valve also changes, which later changes the pump flow rate. The changed pump flow rate consequently expedites the change in the pump pressure. Thus the present invention is very effective especially when an operator wants to speed up the operation.
Further, the present invention uses either a hydraulic pilot type cut valve or an electronic pilot type cut valve. Here, the set pressure adjusting means outputs an electric control signal for controlling the opening of the cut valve according to the control input of the operating means.
Among other cut valve control systems, the aforementioned system controls the cut valve by the electric control signal (cut valve electric control system). This simplifies the constitution of the hydraulic circuit to a great extent.
Further, the set pressure adjusting means of the present invention includes a controller, and a proportional valve for the cut valve for supplying a secondary pressure according to the electric control signal from the controller to the hydraulic pilot type cut valve in the form of a pilot pressure.
Moreover, the present invention includes the regulator for regulating the discharge flow rate of the double hydraulic pump, and the controller outputs a signal to the regulator for changing the pump discharge flow rate.
According to this, as the passing flow rate of the cut valve changes, the pressure inputted in the regulator also changes, which consequently changes the pump flow rate. The changed pump flow rate again speeds up the change in the pump pressure. Therefore, it is very effective especially when an operator wishes to speed up the operation.
In many cases, a pump controlling proportional valve can be used for the regulator.
Also, in the present invention, the remote control valve is used as the operating means, and the remote control pressure withdrawn by the remote control valve is inputted in the controller as an operational signal.
Preferably, the pressure control valve of the present invention is a relief valve. The relief valve is installed in the motor circuit, and its set pressure is variable. That is, the set pressure adjusting means adjusts the set pressure of the relief valve.
Also, in the present invention, the pump pressure control means preferably includes the regulator for regulating the discharge flow rate of the double hydraulic pump, and the controller for sending the command signal concerning the discharge flow rate of the double hydraulic pump out to the regulator in accordance with the control input of the operating means.
The constitution described above is particularly based on the pump control system for controlling the pump flow rate out of other control systems for changing the properties of the pump pressure during the single traveling and the double traveling. When this system is applied, the hydraulic circuit itself does not require any reconstruction, which means that the hydraulic circuit is applicable even to the conventional equipment.
Moreover, the regulator can be a proportional valve for pump control.
Also, in the present invention, the remote control valve is used for the operating means, and the remote control pressure withdrawn by the remote control valve is inputted in the controller in the form of the operational signal.